The mechanical movement (i.e. insertion, withdrawal) and the associated monitoring of the position of the control rods are necessary functions for the operation of a nuclear reactor. Each of the instruments that perform this function typically is terminated with a power cable and one or two position indication cables that transmit signals from the instrument back to processing units, typically located in a control room. As used herein, the term instrument may also include a sensor or sensing device. Known rod position indicator cable systems, such as the one depicted in FIGS. 1 and 2, typically include multi pin connector disconnect points 10 located at the top of the nuclear reactor vessel head 12 and at the reactor cavity wall 14 poolside. Additional disconnect points 10 may also be located at other points between the vessel head 12 and the cavity wall 14. The multi pin connector disconnect points 10 allow each of the interconnecting cable sections 16 to be removed from corresponding sensing instruments 18 to allow for the disassembly of the reactor vessel 8 for refueling. The typical reactor vessel 8 includes on the order of magnitude of 100 or more of these cable assemblies.
The removal and installation of the cable sections 16 is generally part of the “critical path” schedule for a refueling outage and generally requires the services of a specially trained crew of technicians during both the initial and concluding stages of the refueling outage in order to complete the work. Typically, such work can take up to an entire shift to complete. In total, the manipulation of the signal cable sections 16 may occupy an entire day of a 30 day outage. Given an estimated cost of $20,000 to $25,000 per hour of lost critical path time, this one day period would represent a cost of approximately $500,000 per refueling outage without even taking into consideration the cost of the trained work crew.
Additionally, the repeated manipulation of the signal cables increases the potential for damage, leading to the need to repair and/or replace the cables and/or the related hardware. Furthermore, the manipulation of the signal cables must be carried out in a radiation area located above the reactor vessel. Elimination of this work scope would thus eliminate the radiation exposure associated with this work activity.
Accordingly, there exists room for improvement in the system and method for monitoring the position of the control rods and other reactor conditions.